It's not that they are mean exactly. People wouldn't keep them if they were mean. But they have been bred for aggression, and that part of their nature can come out- unexpectedly. More so than for other breeds of dog.
I suppose every animal has a mean streak to it..as do humans, but if one treats a pet with respect and teaches with love, even a pit bull can be a pet, but by nature, pit bulls are aggressive I believe.
I love how " I have one, and he's just so sweet" answers judge a breed by a single dog. Pits were bred to handle bulls and bring them down if necessary. They are working dogs with an aggressive streak and it takes a committed owner to handle them. They are like other dogs in that they are prone to go after children since they are pretty much eye to eye but unlike other breeds, pits are more prone to do great damage to a child